Photoengraver&#39;s etching bath



Feb. 1955 A. J. POWERS, JR., ETAL 2,701,183

PHOTOENGRAVERS ETCHING BATH Filed Feb. 17, 1951 70 M M INVENTORS:

AUGUST/N J POWER-3J1 24 BY Geo/re: A; BuTTR,JR.

A TTORNEKS United States Patent PHOTOENGRAVERS ETCHING BATH Augustin .1.Powers, Jr., Roslyn Heights, and George A. Butter, Jr., Levittown, N.Y., assignors to Powers Chemco, Inc., a corporation of New YorkApplication February 17, 1951, Serial No. 211,518

3 Claims. (Cl. 23-253) The invention relates to the art ofphotoengraving and more particularly to the etching process in preparingthe photoengraved plate for use.

It further relates to a device by which the strength of an etching bathacid solution may be accurately determined so that a plate subjected tothe action of the tested etching solution during the time periodindicated 3y tie device will be etched to a predetermined desiredObjects and advantages of the invention will be set forth in parthereinafter and in part will be obvious herefrom, or may be learned bypractice with the invention, the same being realized and attained bymeans of the instmmentalities and combinations pointed out in theappended claims.

The invention consists in the novel parts, constructions, arrangements,combinations and improvements herein shown and described.

The accompanying drawings, referred to herein and constituting a parthereof, illustrate two embodiments of the invention, and together withthe description, serve to explain the principles of the invention.

Of the drawings:

Figure 1 is a front elevation of an etching bath testing device showinga metal test strip in place therein;

Figure 2 is a side elevation of the device shown in Figure 1;

Figure 3 is a plan view of a metal test strip as used in the testingdevice;

Figure 4 is a fragmentary vertical section through an etching bath trayshowing the device partially immersed in the acid;

Figure 5 is a front elevation of an alternate form of testing devicewith a test strip clamped therein;

Figure 6 is a fragmentary front elevation of the lower portion of thedevice shown in Figure 5 but illustrates the jaws in the positionassumed when the test strip is to be inserted or released; and

Figure 7 is a vertical section taken along the line 77 of Figure 5.

As presently practiced, the strength or concentration of an acidsolution to be used for etching halftone or line photoengravings isroughly determined by a guess by a skilled operator that the processingof a certain number of plates has exhausted the usefulness of thesolution, or alternatively by noting the depth to which a plate isetched during a normal time of etching. Such rough determination orguesswork results in ineflicient use of the etching solution as well aspossible adverse variations in the desired depth of etch in successiveplates.

The use of the invention as described herein enables an etcher toperform a simple test which will indicate the exact time that the acidbeing tested will take to produce an etch of desired depth. Thus, onlywhen the time to produce a desired depth of etch becomes longer thandeemed efiicient is it necessary to renew the etching solution.

The invention consists of a scissors or pincher-like device formed,partially or wholly, of material which is nonetchable by the solution tobe tested. The jaws of the device are spring-urged away from each otherand provided with hooks or clamps for attaching a specially formedetchable metal test strip. The strip is of such a length that whenattached to the jaws the strip is under spring tension. The centralportion of the test strip is so shaped and proportioned that whenimmersed in the "ice etching acid the strip will break at this portionwhen it is etched through. The breaking of the strip permits the jaws tospring apart and thus indicate by visible, auditory or other means theexact moment of the break. The time interval between the time the teststrip was immersed in the acid to its time of breaking gives ameasurement which may be used to determine the length of time aphotoengraving must be subjected to the etching solution to produce adesired depth of etch.

It will be understood that the foregoing general description and thefollowing detailed description as well are exemplary and explanatory ofthe invention but are not restrictive thereof.

Referring now to the drawings and more particularly to Figures 1 to 4,the test strip holding device consists of a pair of jaw members 10 and12 pivoted to each other by a pin 14. Each jaw is extended beyond thepivot to form a handle 16 or 18.

Recesses 20 in each jaw and handle member at the pivot portion permitnesting of the two members and alignment of the jaws and handles in thesame plane.

Either the lower portion or the entire test strip holding device shouldbe constructed of an acid resisting metal, plastic or similar material,and for use with nitric acid, stainless steel is a suitable material,while for a ferric chloride bath, the device should be constructed ofpolystyrene, rigid phenolic resin, cellulose acetate or otherappropriate relatively non-corrodible material.

Each of the jaws 10 and 12 is provided with a project ing hook 22 withthe open end of each hook facing away from the other. Jaw 10 is furtherprovided with an offset extension plate 24 which projects downwardly andthen laterally to a point beneath and beyond the other jaw 12 where anupwardly projecting lug 26 is formed in the plane of jaw 12 to act as astop for limiting the spreading of the jaws. Extension 24 also acts as asupport standard for the device to insure that a test strip 28 carriedby hooks 22 is above any contaminating sediment which may be in thebottom of the etching bath tray.

Means for urging the jaws 10 and 12 away from each other to the limit ofstop lug 26 is provided by a coiled compression spring 30 seated inrecesses in the facing sides of the handles 16 and 18.

The means for testing the etching strength of the acid bath consists ofa test strip 28 of metal capable of being etched by the acid in use suchas copper, zinc or magnesium. A narrow neck 32 of the strip 28 is soproportioned in width and thickness that the time necessary for the acidto etch through the neck 32 is in direct proportion to the timenecessary for that same acid to etch a photoengraving plate to a desireddepth. Thus as an acid bath weakens through continued use a longer timeis necessary to etch the strip 28 to its breaking point and acorresponding increase in time is thereby indicated for the processingof the plate to produce the same desired etched depth.

The enlarged ends of strip 28 are provided with slots 34 which areadapted to be slipped over hooks 22 when the jaws are squeezed togetherthe necessary amount. The distance between the slots 34 is such that jaw12 is held a small distance away from the stop lug 26 when the strip ismounted on the hooks 22 of the device. When the strip 28 breaks, thejaws 10 and 12 snap apart and the lug 26 sharply strikes jaw 12 with anappreciable ping if the jaws are made of metal or a visible jarring ofthe device if softer or non-sound producing material forms the jaws,thus notifying the operator that the end of the time period beingmeasured has arrived.

Additional means may be employed to indicate the breaking of strip 28and one such means may be a bell 36 attached to the handle 16 andadapted to be struck by a sensitive spring mounted clapper 38 secured onthe handle 16 adjacent the bell 36. Thus as the jaw 10 suddenly strikesstop 26, when strip 28 breaks, the clapper 38 is caused to vibrate andring the bell 36.

As illustrated in Figure 4 the device when in use is placed in theetching bath tray 40 with the strip immersed in the acid 42 and thesupport standard or extension 24 resting on the bottom of tray 40 whilethe handles 16 and 18 rest against a tray side. After the strip 28 hasbroken, the ends remaining on hooks 22 may be shaken off by the operatorwithout touching them and a new strip easily hooked in place.

An alternate form of the testing device is illustrated in Figures 5, 6,and 7 wherein the hooks 22 of the form previously described are replacedby cam clamps. As shown the device comprises jaws 50 and 52 and handles54 and 56 which may be channel shaped and pivoted to each other at 58 atwhich point the web of jaw 50 and handle 56 is cut away to permit theother jaw 52 and handle 54 to pass therethrough. The jaws are urgedapart by a leaf spring 60 secured on the web of handle 56 and pressingagainst the web of handle 54. A plate 62 having a foot 64 is secured tothe lower end of jaw 50 and extends downward below the jaw end andlaterally towards a point below the other jaw 52. A combination clampactuating and stop lug 66 is struck up from the plate 62. A plate 68,similar to plate 62, is secured on jaw 52 and provided with a turned uplug 70 to actuate a second clamp. The spread of the jaws 50 and 52, asurged by spring 60, is limited by an edge 74, provided on plate 68,striking the stop lug 66 on plate 62.

Means for clamping a test strip 28 on the ends of jaws 50, 52 areprovided whereby the strip is held thereon and subjected to the tensionproduced by the jaw spreading spring 60. As embodied a pair of clamps'76 are provided, one of which is pivoted on plate 62 and the other onplate 68, at a point just beneath the web portion of the jaw associatedwith the respective plates. A cam surface 78 on the upper end of eachclamp 76 is adapted to engage the adjacent jaw end as the clamp ispartially rotated by the urging of a relatively strong leaf spring 80which may be attached at one end to the jaw and have its free end pressupon the free end of clamp 76.

As shown in Figure 6 the cam surfaces 78 on clamps 76 are caused to moveaway from their adjacent jaw ends as jaws 50, 52 are brought towardseach other by squeezing the handles 54, 56. This is caused by stop lug66 on plate 62 striking the free end of the right hand clamp 76 and thelug 70 on plate 68 striking the free end of the left hand clamp 76 thusrotating the clamps in opposite directions. A test strip 28, which maybe in the form shown in Figure 3 or a simple ribbon of etchable metal,such as copper, zinc or magnesium, may then be placed in the device sothat one end of the strip is between the end of jaw 50 and its clamp 76and the opposite end between the end of jaw 52 and its clamp 76. Thehandles 54, 56 may then be released thus permitting clamps 76 to rotate,oppositely, as lugs 66 and 70 move away from them thereby causing therespective cam surfaces 78 to pinch the strip 28 against each jaw end.Further spreading of the jaws is then arrested. Figure illustrates thedevice in the condition just described.

The device is now placed in the acid bath in a manner similar to thatshown in Figure 4 and when the metal strip 28 is etched through andbreaks, the spring 60 snaps the jaws 50, 52 apart. As edge 74 on plate62 strikes stop lug 66 on plate 62 the jaws come to a sudden stop andgive a visual or auditory signal indicating the end of the test time.The broken ends of strip 28 may be readily freed from the device merelyby squeezing the handles of the device.

Various metals may be used for making the test strip 28 and in practicethe selected metal may be the same as that from which the photoengravingplate is made, as, for instance, if a copper plate is to be etched in aferric chloride bath the strip 28 could be copper of the samecomposition as the plate and the neck portion 32 of the strip would havea width and thickness of previously calculated and tested size so thatits breaking time is a direct indication of the depth to which theferric chloride being tested will etch the copper photoengraving plate.Similarly if a zinc base plate and nitric acid are the materials in usea test strip 28 of appropriate size may be made of zinc having the samecomposition as the plate.

It is also contemplated that the metal of the test strip 28 may be of adifferent composition than that of the photoengraving plate as, forexample, magnesium ribson, in which case the time to etch the strip to abreaking point may be shorter than the time necessary for a desireddepth of plate etch but which is, nevertheless, in direct proportion tothat time. In actual practice, the size and material of the test strip28 are so correlated to the normal strength of the etching bath that thestrip is normally etched to its breaking point in a period of fromfifteen to forty-five seconds. Shorter times than fifteen seconds areusually undesirable due to the possible errors in etching at such shorttime, and longer periods than forty-five seconds are unnecessarily long.

The invention in its broader aspects is not limited to the specificmechanisms shown and described but departures may be made therefromwithin the scope of the accompanying claims without departing from theprinciples of the invention and without sacrificing its chiefadvantages.

What is claimed is 1. A photoengravers etching bath testing deviceincluding in combination a pair of scissor-like levers pivoted togetherat an intermediate point, means engaging said levers for constantlyurging the ends of the levers away from each other, said lever endsbeing formed with spring closing jaws for holding a metal test strip tobe etched at portions spaced apart along said strip so that a portion ofsaid strip between said held positions is freely available to beattacked by an etching solution, and means for opening the jaws as thelevers are moved together, said strip being held in constant tension asthe ends of said levers are resiliently urged apart.

2. A testing device as claimed in claim 1 in which means are provided onthe levers for spacing the test strip from the bottom of the etchingbath.

3. A photoengravers etching bath testing device, including incombination a pair of elements for engaging and holding at spaced pointsa metal test strip to be etched, whereby a portion of said strip betweensaid points is freely available to be attacked by an etching solution,means for constantly resiliently urging said elements away from eachother whereby a test strip is held in constant tension when held by saidelements, and means for spacing the test strip so held from the bottomof an etching bath container as the test strip is immersed in theetching bath, said last means comprising a plate connected to one ofsaid elements and extending toward the other said element said platehaving a substantially straight surface disposed below the test stripadapted to be seated on the bottom of the etching bath container.

References Cited in the file of this patent UNITED STATES PATENTS859,925 Des Isles July 16, 1907 1,081,786 Sublett Dec. 16, 19131,520,716 Judd Dec. 30, 1924 2,042,457 Conn June 2, 1936 2,270,389Straub Jan. 20, 1942 2,319,377 Wallace et al. May 18, 1943 2,601,839Kucewicz July 1, 1952 FOREIGN PATENTS 31,891 Germany Nov. 4, 1884 13,650Great Britain May 18, 1895

1. A PHOTOENGRAVER''S ETCHING BATH TESTING DEVICE INCLUDING INCOMBINATION A PAIR OF SCISSOR-LIKE LEVERS PIVOTED TOGETHER AT ANINTERMEDIATED POINT, MEANS ENGAGING SAID LEVERS FOR CONSTANTLY URGINGTHE ENDS OF THE LEVERS AWAY FROM EACH OTHERS, SAID LEVER ENDS BEINGFORMED WITH SPRING CLOSING JAWS FOR HOLDING A METAL TEST STRIP TO BEETCHED AT PORTIONS SPACED APART ALONG SAID STRIP SO THAT A PORTION OFSAID STRIP BETWEEN SAID HELD POSITIONS IS FREELY AVAILABLE TO BEATTACKED BY AN ETCHING SOLUTION, AND MEANS FOR OPENING THE JAWS AS THELEVERS ARE MOVED TOGETHER SAID STRIP BEING HELD IN CONSTANT TENSION ASTHE ENDS OF SAID LEVERS ARE RESILIENTLY URGED APART.